I've found what appears to be a great local company to install both a softener and an RO. Standardized parts, pricing, warranty, service, longevity, and answers to all my questions match up to what I've read here and elsewhere about this industry and selecting a system.

That is, except for their sizing recommendation, which seems off to me. That said, I am hardly an expert so I'd like to get a 2nd opinion from this forum.

House is 2.5 bathrooms, with an additional bathroom and wetbar sink to be added in the lower level within the next year for a total of 3.5 bathrooms that I am planning for.

Household is 2 adults, 1 toddler, and 1 on the way. House is on city water and water usage per month (in the winter to try and eliminate landscaping and pool watering costs) is about 5-7k gallons. For the 3 current people that breaks out to 66 gallons per person per day on average (6k/3/30day). I might still be counting some landscaping water in there though.

Water company report says hardness is between 7 and 20. Softener company says that their experience leads them to plan for 25-30 for this area to avoid service calls.

Company is recommending their "48k size", which they say translates to 1.5 cu ft of resin. They claim regen is designed for about every 5 days with a targeted 7lb per cu ft of salt usage per regen. Of course, with a Clack WS1 it is metered on demand and they say they plan for about 1800 gallons of use between regens. Also quote a 20-22gpm flow rate. I also picked up on what was somewhat of a careless attitude when it comes to salt/water efficiency, so that makes me want to question their numbers even more.

Flow rate looks good, but I'm not sure if the rest of the numbers add up to me. My main concern is that 1.5 cu ft is too little based on what I've seen here. I think I should mostly be concerned about getting the cu ft right, and then I can tweak the Clack programming as desired. Does that sound right?

Overall I'm looking for a size that will meet my current needs without too much waste, but can grow as my family grows and I can reprogram the Clack as needed to adjust for that.

The numbers look good to me. If you go bigger, than the days between regens goes up. You can go beyond what recommended days (7) between regens which is not good for the resin. IMO salt is cheap. You might use $51.00 of salt per year based on your numbers.

Thanks for the response. If I run my numbers through Gary's calculator using 4 people at 66gpd avg, with 20 gpg, I get a min cu ft recommendation of 2.5. Using the higher 25 gpg, the recommendation is 3.0, which is double what the company is recommending. This type of difference is what is sparking my concern.

Also, if I have a 1.5 cu ft regen at 7 lb/ft, then that's 10.5 lbs salt per regen, and if I match that up with Gary's charts, that looks to be about 33000 grains worth. Is that really a 48k system?

It's on demand generation so it's programmed to regen after, say 1800 gallons pass through the system. Is there a calendar setting as well that forces regen if you don't hit 1800 gallons by a certain number of days?

A 1.5 cuft has a constant SFR of 12 gpm. You can't get 48K out of 1.5 cuft except the first time you use it IF you run the resin to total bed exhaustion but, you can't regenerate it back to more than 45K. And to do that you must use 15lbs per cuft foot; 22.5 lbs total and you should do it twice with no water use during or between the 2 regenerations so you get it back to 45K.

Now 45,000/22.5 lbs gets you a salt efficiency of 2000 grains/lb. So you would program say your 33K/3333 grains/lb for a total of 9.9 lbs and efficiency of 3333 grains/lb. 66*4= 264 gals/day *20 gpg = 5280 *8days = 42240 grains rounded up to 43K. So a 1.5 cuft is too small and you'd go to a 2.0 cuft and use 43000/3333 grains/lb =12.9 rounded to 10lbs of salt total per regeneration.

I used 8 days for the service run between regenerations and you should too. Set teh calendar override at day 8. You should use the water company's max hardness in their system which I have; 20 gpg. The 25 or more gpg you used causes a higher K pf capacity, a larger softener, or reduced salt efficiency and you don't need a larger constant SFR.

The 2.0 cuft gives you a constant SFR of 13 gpm. And without any large jetted etc. tubs, body sprays or over sized shower heads, you shouldn't need more. And as the kids get out there to about 12+ and 2-3 showers are wanted at once, you can do laundry and dishes when no other water is being used and still be under 13 gpm.

The numbers look good to me. If you go bigger, than the days between regens goes up. You can go beyond what recommended days (7) between regens which is not good for the resin. IMO salt is cheap. You might use $51.00 of salt per year based on your numbers.

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The days between regenerations are adjustable to whatever number you want.

The same for the K of capacity and lbs of salt used.

Inefficient sizing and programming also uses much more water than a correctly sized and programmed identical softener.

And to say "salt is cheap" because you can't learn to size and program correctly is a bad way to do business.

Have you learned what CV.... any number on a control valve spec sheet means yet?

Thanks for the reply. Your math makes sense to me. For 1.5 cu ft, the most efficient setting of 9.9 lbs would give me 33k grains to use, which at 20gpg, is about 1620 gallons. Assuming 7 days, that gives 231 gallons per day. At 3 people (current household) that is 77 g pp pd. At 4 people that is 57 g pp pd. I'm estimating I won't hit 1600 gallons of usage until the kids are much older - say at least 10 years from now. I know some resins have 25 yr warranties and such, but won't it be likely to replace the resin by then anyway? Does it make sense to go bigger today, if I'm likely to replace the resin anyway between year 10 and 15, especially considering the chlorine in the city water.

I think I'm also going to do a more exact test of daily water usage excluding the landscaping/pool instead of estimating from the monthly water bill.

I'm not saying to soften irrigation water, in fact, I am specifically trying to exclude it from my calculations. That said, I'm not sure how my house is plumbed. For all I know, the outside hose bib is within the soft water loop. I don't know of anyway to determine this without installing the softener or putting a shutoff valve on the soft water loop.

I think 60 gpd is a great rule of thumb, but if I can do an exact measurement with reasonable projections, I'd rather go with that. Every family is different.

At this point it appears I am right on the bubble between 1.5 and 2.0 cu ft, and future growth may push me over the edge.

And Gary, I've read your signature link at least 10 times now. Since you don't state which assumptions I'm making are incorrect, I'm only left to guess that you are trying to get me to put a higher weight on SFR. The thing I don't get is why 1.5cf is 12gpm and 2.0cf is only 13gpm. Then 2.5 jumps up to like 18gpm. If 13gpm is plenty (as you state above), then 12gpm should be good enough.

A 1.0' is a 9"x54' tank. 1.5' is a 10"x54". 2.0 is a 12"x 52'. 2.5' is a 13"x 54" tank.

The depth of the bed is the critical part. So going from a 9" to 10" is much less spreading out of the bed and you increase the depth much more than going from a 10" to 12" tank, hence the not so much increase in constant flow rate going to a 2" wider tank. Then from a 12" to 13" is only 1" so much more added depth and a jump to 18 gpg. Another part of it is that as the tank gets wider, the velocity of the flow slows down which allows more time for the water to be in contact with the exchange sites on the resin beads.

Use 60 gals/person/day and if the history of the valve shows you use more all you do is adjust the K of capacity etc.. If you guess and come up with more gallons and you're wrong you buy a larger softener than needed and there is nothing you can do about it. For a family of four, you wouldn't buy a 9 passenger van over a 6 passenger minivan unless you were going to consistently haul something other than a normal family does, would you?

If your watering bib is on softened water, you change it to hard water or run a new hard water line or stop watering from that bib. The best way to find out which it is is to install the correct size softener and test the water. Many loops installed when a house is built does not allow softening of outside hose bibs or irrigation systems.

BTW, I have 24 years experience and 7 years selling to people from Puerto Rico across the US and Canada to Alaska. And 99% of families use 60 gals/person/day. That's actual knowledge, not a rule of thumb.

Gary, thanks for the explanation regarding tank size. I didn't realize cu ft flow rate was dependent on tank size. I should probably ask this question of the dealer since I don't know the tank size they use.

IMHO, your van analogy is invalid because a family member will always take up the same seating as a child as they will as an adult. However with water usage, as they age, the water usage will naturally increase. Now surely, it will eventually reach an adult like 60 gpd, but how many years before that happens? 10? 12 ? 15? The question I'm asking myself is 'why buy for a need I won't have for another 10-15 years?' That said, I do understand the gas tank analogy with regard to resin and I understand the argument that it doesn't hurt to err a little on the larger size.

The only point where I disagree with you is that an infant/child does not use the same amount of water per day as an adult. And since my children are very young, it does not necessarily make sense to me to size them as if they were adults.

Regarding your statement "if you size correctly, there is no err on the larger size", that would only be true if you believe the larger size was the correct size to begin with. And it is clear to me that is what you believe, and I certainly respect your years of experience, which is why I am second guessing my dealer's recommendation of 1.5cuft and why I am taking a closer look at my actual water usage.

1.5 cubic to 2 cubic single should do very well..
Your local dealer most likely has more years in that area than most of us here in treating your water.. any number of us might have many years in water treatment but I know little to nothing of water in AZ....

If a single is bought now and 5-7 years from now you feel that a twin would be better then an upgrade most likely would be the way to go as you already have the one tank and the salt tank,, and depending on the system that you go with .. might even have the meter and bypass already plumbed in ..

The only point where I disagree with you is that an infant/child does not use the same amount of water per day as an adult. And since my children are very young, it does not necessarily make sense to me to size them as if they were adults.

Regarding your statement "if you size correctly, there is no err on the larger size", that would only be true if you believe the larger size was the correct size to begin with. And it is clear to me that is what you believe, and I certainly respect your years of experience, which is why I am second guessing my dealer's recommendation of 1.5cuft and why I am taking a closer look at my actual water usage.

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What happens if you use say 30 gallons less per day than 60 gals/person/day? And what do you do if you used 30 gals more per day?